Method of producing anisotropic conductive film and anisotropic conductive film

ABSTRACT

Anisotropic conductive film produced that a light-transmitting transfer die having openings with conductive particles disposed therein is prepared, and photopolymerizable insulating resin squeezed into openings to transfer conductive particles onto the surface of the photopolymerizable insulating resin layer, first connection layer is formed which has a structure in which conductive particles are arranged in a single layer in a plane direction of photopolymerizable insulating resin layer and the thickness of photopolymerizable insulating resin layer in central regions between adjacent ones of the conductive particles is smaller than thickness of photopolymerizable insulating resin layer in regions in proximity to conductive particles; first connection layer is irradiated with ultraviolet rays through light-transmitting transfer die; release film is removed from first connection layer; second connection layer is formed on the surface of first connection layer opposite to light-transmitting transfer die; and third connection layer is formed on the surface of first connection layer.

TECHNICAL FIELD

The present invention relates to a method of producing an anisotropicconductive film and the anisotropic conductive film.

BACKGROUND ART

Anisotropic conductive films are widely used to mount electroniccomponents such as IC chips. In recent years, for the purpose ofimprovement in connection reliability and insulating properties,improvement in particle capturing efficiency, a reduction in productioncost, etc., an anisotropic conductive film in which conductive particlesfor anisotropic conductive connection are arranged in a single layerwithin an insulating adhesive layer has been proposed from the viewpointof application to high-density mounting (Patent Literature 1).

This anisotropic conductive film is produced as follows. First, atransfer die having openings is used to hold conductive particles in theopenings, and an adhesive film having an adhesive layer for transferformed thereon is pressed against the transfer die to primary-transferthe conductive particles to the adhesive layer. Next, a polymer filmserving as a component of the anisotropic conductive film is pressedagainst the conductive particles adhering to the adhesive layer, andheat and pressure are applied thereto to secondary-transfer theconductive particles to the surface of the polymer film. Next, anadhesive layer is formed on the surface of the polymer film on which theconductive particles have been secondary-transferred so as to cover theconductive particles, whereby the anisotropic conductive film isproduced.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No.2010-33793

SUMMARY OF INVENTION Technical Problem

In the anisotropic conductive film in Patent Literature 1 that isproduced using the transfer die having openings, the connectionreliability, insulating properties, and particle capturing efficiency ofthe anisotropic conductive film may be expected to be improved to someextent so long as the primary transfer and the secondary transfer havebeen successfully done. However, generally, the adhesive film used forthe primary transfer has relatively low adhesion in order to facilitatethe secondary transfer, and the area of contact between the adhesivefilm and the conductive particles is small. Therefore, it is feared thatthe total operation efficiency in the operation of the primary transferand the operation of the secondary transfer may deteriorate because of,for example, the occurrence of conductive particles notprimary-transferred, detachment of conductive particles from theadhesive film after the primary transfer, and positional displacement ofconductive particles on the adhesive film.

When the adhesion of the adhesive film is increased to some extent toallow the conductive particles to be stably held in the adhesive film inorder for the primary transfer operation to proceed faster and moresmoothly, secondary transfer of the conductive particles to the polymerfilm becomes difficult. When the film properties of the polymer film areenhanced in order to avoid the above problem, another problem arises inthat the conduction resistance of the anisotropic conductive filmincreases and its conduction reliability is also reduced. When ananisotropic conductive film is produced using the transfer die havingopenings described above, the primary transfer and the secondarytransfer may not in fact always be successfully done. Therefore, atpresent, there still is a strong demand for an anisotropic conductivefilm having favorable connection reliability, favorable insulatingproperties, and favorable particle capturing efficiency simultaneously.

It is an object of the present invention to solve the foregoing problemsin the conventional technology. More specifically, the object is toallow an anisotropic conductive film having favorable connectionreliability, favorable insulating properties, and favorable particlecapturing efficiency to be produced when producing an anisotropicconductive film including conductive particles arranged in a singlelayer utilizing a transfer die having openings.

Solution to Problem

The present inventor has found that the above object can be achieved bythe following method, and thus the present invention has been completed.Specifically, a light-transmitting transfer die having openings is usedas the transfer die for producing an anisotropic conductive film.Conductive particles arranged in a single layer are transferred to aninsulating resin layer used for the anisotropic conductive film directlyfrom the transfer die without primary transfer of the conductiveparticles to an adhesive film. The conductive particles are transferredsuch that the thickness of the insulating resin layer in central regionsbetween adjacent ones of the conductive particles is smaller than thethickness of the insulating resin layer in regions in proximity to theconductive particles. The insulating resin holding the conductiveparticles is irradiated with ultraviolet rays through thelight-transmitting transfer die to photo-cure the insulating resin, andthen the insulating resin layer in which the conductive particles arearranged in a single layer is sandwiched between insulating resin layersfunctioning as adhesive layers.

Accordingly, the present invention provides a method of producing ananisotropic conductive film having a three-layer structure in which afirst connection layer is held between a second connection layer and athird connection layer, which are each formed mainly of an insulatingresin. The method of producing includes the following steps (A) to (F).

<Step (A)>

The step of disposing conductive particles within openings formed in alight-transmitting transfer die and placing, on the transfer die, aphotopolymerizable insulating resin layer formed on a release film suchthat the photopolymerizable insulating resin layer faces a surface ofthe transfer die on which the openings are formed.

<Step (B)<

The step of applying pressure to the photopolymerizable insulating resinlayer through the release film to squeeze a photopolymerizableinsulating resin into the openings to thereby transfer the conductiveparticles onto a surface of the photopolymerizable insulating resinlayer, whereby a first connection layer is formed, the first connectionlayer having a structure in which the conductive particles are arrangedin a single layer in a plane direction of the photopolymerizableinsulating resin layer and in which the photopolymerizable insulatingresin layer in central regions between adjacent ones of the conductiveparticles has a thickness smaller than that of the photopolymerizableinsulating resin layer in regions in proximity to the conductiveparticles.

<Step (C)>

The step of irradiating the first connection layer with ultraviolet raysthrough the light-transmitting transfer die.

<Step (D)>

The step of removing the release film from the first connection layer.

<Step (E)>

The step of forming the second connection layer, being formed mainly ofthe insulating resin, on a surface of the first connection layer that isopposite to the light-transmitting transfer die.

<Step (F)>

The step of forming the third connection layer, being formed mainly ofthe insulating resin, on a surface of the first connection layer that isopposite to the second connection layer.

The present invention also provides a method of connecting a firstelectronic component to a second electronic component by anisotropicconductive connection using the anisotropic conductive film obtained bythe above-described production method, the method including temporarilyapplying the anisotropic conductive film to the second electroniccomponent through the third connection layer of the anisotropicconductive film, mounting the first electronic component on thetemporarily applied anisotropic conductive film, and performingthermocompression bonding through the first electronic component. Thepresent invention also provides an anisotropic conductive connectionstructure obtained by this connection method.

The present invention also provides an anisotropic conductive filmhaving a three-layer structure in which a first connection layer is heldbetween a second connection layer and a third connection layer, whichare each formed mainly of an insulating resin, wherein

-   -   a boundary between the first connection layer and the third        connection layer is undulated,    -   the first connection layer has a structure in which conductive        particles are arranged on a side facing the third connection        layer in a single layer in a plane direction of an insulating        resin layer, and the thickness of the insulating resin layer in        central regions between adjacent ones of the conductive        particles is smaller than the thickness of the insulating resin        layer in regions in proximity to the conductive particles.

In a preferred embodiment of the anisotropic conductive film, the firstconnection layer is a thermal- or photo-radical polymerizable resinlayer containing an acrylate compound and a thermal- or photo-radicalpolymerization initiator or a layer obtained by subjecting the thermal-or photo-radical polymerizable resin layer to thermal- or photo-radicalpolymerization; or a thermal- or photo-cationic or anionic polymerizableresin layer containing an epoxy compound and a thermal- orphoto-cationic or anionic polymerization initiator or a layer obtainedby subjecting the thermal- or photo-cationic or anionic polymerizableresin layer to thermal- or photo-cationic or anionic polymerization. Inanother preferred embodiment, the conductive particles dig into thethird connection layer. In another preferred embodiment, the degree ofcure of the first connection layer in regions positioned between theconductive particles and a surface of the first connection layer thatfaces the second connection layer is lower than the degree of cure ofthe first connection layer in regions positioned between adjacent onesof the conductive particles. In another preferred embodiment, theminimum melt viscosity of the first connection layer is higher than theminimum melt viscosity of the second connection layer and the minimummelt viscosity of the third connection layer. In another preferredembodiment, the ratios of the minimum melt viscosity of the firstconnection layer to the minimum melt viscosity of the second connectionlayer and to the minimum melt viscosity of the third connection layerare each 1:4 to 400.

Advantageous Effects of Invention

The present invention is a method of producing an anisotropic conductivefilm having a three-layer structure in which a first connection layer isheld between an insulating second connection layer and an insulatingthird connection layer. In this production method, when the anisotropicconductive film is produced using the transfer die having openings, theconductive particles arranged in a single layer in the transfer die aretransferred directly from the transfer die to the photopolymerizableinsulating resin layer used for the first connection layer constitutingthe anisotropic conductive film without primary transfer to an adhesivefilm. In addition, the conductive particles are transferred such thatthe thickness of the photopolymerizable insulating resin layer incentral regions between adjacent ones of the conductive particles issmaller than the thickness of the photopolymerizable insulating resinlayer in regions in proximity to the conductive particles (i. e., suchthat the conductive particles protrude from the first connection layer).When the protrusions are disposed on the side facing the thirdconnection layer to be placed on, for example, a circuit board on whichan electronic component such as an IC chip is mounted, particlecapturing efficiency can be improved. By irradiating thephotopolymerizable insulating resin layer with ultraviolet rays throughthe light-transmitting transfer die, the photopolymerizable insulatingresin layer which holds the conductive particles and is to become thefirst connection layer can be photo-cured while being held in thetransfer die, and the degree of cure of the photopolymerizableinsulating resin layer in potions shaded from the ultraviolet rays bythe conductive particles can be relatively reduced. In this manner,while excessive movement of the conductive particles in a planedirection is prevented, the ease of pushing the conductive particles canbe improved, and favorable connection reliability, favorable insulatingproperties, and favorable particle capturing efficiency can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram illustrating step (A) in an anisotropic conductivefilm production method of the present invention.

FIG. 1B is a diagram illustrating step (A) in the anisotropic conductivefilm production method of the present invention.

FIG. 2A is a diagram illustrating step (B) in the anisotropic conductivefilm production method of the present invention.

FIG. 2B is a diagram illustrating step (B) in the anisotropic conductivefilm production method of the present invention.

FIG. 3 is a diagram illustrating step (C) in the anisotropic conductivefilm production method of the present invention.

FIG. 4 is a diagram illustrating step (D) in the anisotropic conductivefilm production method of the present invention.

FIG. 5 is a diagram illustrating step (E) in the anisotropic conductivefilm production method of the present invention.

FIG. 6 is a cross-sectional view of the anisotropic conductive film ofthe present invention obtained by step (F) in the anisotropic conductivefilm production method of the present invention.

FIG. 7 is a partial cross-sectional view of the anisotropic conductivefilm obtained by the production method of the present invention.

FIG. 8 is a cross-sectional view of the anisotropic conductive film ofthe present invention.

DESCRIPTION OF EMBODIMENTS <<Method of Producing Anisotropic ConductiveFilm>>

Each of steps in the anisotropic conductive film production method ofthe present invention will be described in detail.

An example of the anisotropic conductive film production method of thepresent invention will next be described. This production methodincludes the following steps (A) to (F). These steps will be describedone by one.

<Step (A)>

As shown in FIG. 1A, conductive particles 4 are disposed in openings 21formed in a light-transmitting transfer die 20. Then aphotopolymerizable insulating resin layer 10 formed on a release film 22such as a release-treated polyethylene terephthalate film is placed onthe transfer die 20 so as to face the surface of the transfer die 20that has the openings 21 formed thereon, as shown in FIG. 1B.

The light-transmitting property of the transfer die 20 means theproperty of allowing ultraviolet rays to pass therethrough. Noparticular limitation is imposed on the level of the light-transmittingproperty. From the viewpoint of allowing photopolymerization to proceedrapidly, the ultraviolet transmittance measured using aspectrophotometer (measurement wavelength: 365 nm, optical path length:1.0 cm) is preferably 70% or higher.

The transfer die 20 is prepared by forming the openings in a transparentinorganic material such as ultraviolet transmitting glass or an organicmaterial such as polymethacrylate using a known opening forming methodsuch as photolithography. The above transfer die 20 may have aplate-like shape, a roll-like shape, etc.

The openings 21 of the transfer die 20 are used to accommodate theconductive particles thereinside. Examples of the shape of the openings21 may include a cylindrical shape, polygonal prism shapes such as aquadrangular prism shape, and pyramid shapes such as a quadrangularpyramid shape.

Preferably, the arrangement of the openings 21 is a regular arrangementsuch as a lattice arrangement or a staggered arrangement.

The ratio of the average particle diameter of the conductive particles 4to the depth of the openings 21 (=the average particle diameter of theconductive particles/the depth of the openings) is preferably 0.4 to 3.0and more preferably 0.5 to 1.5, from the viewpoint of the balancebetween improvement in transferability and retainability of theconductive particles.

The ratio of the diameter of the openings 21 to the average particlediameter of the conductive particles 4 (=the diameter of theopenings/the average particle diameter of the conductive particles) ispreferably 1.1 to 2.0 and more preferably 1.3 to 1.8, from the viewpointof the balance between, for example, the ease of accommodation of theconductive particles and the ease of squeezing the insulating resin intothe openings.

The diameter and depth of the openings 21 of the transfer die 20 can bemeasured using a laser microscope.

No particular limitation is imposed on the method of accommodating theconductive particles 4 within the openings 21 of the transfer die 20,and any known method can be used. For example, dry powder of theconductive particles or a dispersion prepared by dispersing the powderin a solvent is sprinkled on or applied to an opening-formed surface ofthe transfer die 20, and then the opening-formed surface is wiped with,for example, a brush or a blade.

<Step (B)>

Next, as shown in FIG. 2A, pressure is applied to the photopolymerizableinsulating resin layer 10 through the release film 22 to squeeze thephotopolymerizable insulating resin into the openings 21, so that theconductive particles 4 are transferred to the surface of thephotopolymerizable insulating resin layer 10 so as to be embeddedtherein. A first connection layer 1 is thereby formed as shown in FIG.2B. Specifically, the first connection layer 1 has a structure in whichthe conductive particles 4 are arranged in a single layer in a planedirection of the photopolymerizable insulating resin layer 10. In thefirst connection layer 1, the thickness t1 of the photopolymerizableinsulating resin layer in central regions between adjacent ones of theconductive particles 4 is smaller than the thickness t2 of thephotopolymerizable insulating resin layer in regions in proximity to theconductive particles 4.

If the thickness t1 of the photopolymerizable insulating resin layer inthe central regions between adjacent ones of the conductive particles 4is excessively smaller than the thickness t2 of the photopolymerizableinsulating resin layer in the regions in proximity to the conductiveparticles 4, the conductive particles 4 tend to move excessively duringanisotropic conductive connection.

If the thickness t1 is too large, the ease of pushing the conductiveparticles tends to deteriorate. In both the cases, it is feared thatparticle capturing efficiency may deteriorate. Therefore, the ratio ofthe thickness t1 to the thickness t2 is preferably 0.2 to 0.8 and morepreferably 0.3 to 0.7.

If the absolute value of the thickness t1 of the photopolymerizableinsulating resin layer is too small, it is feared that the firstconnection layer 1 may be difficult to form. Therefore, the absolutethickness is 0.5 μm or more. If the absolute thickness is too large, itis feared that the insulating resin layer may not be easily eliminatedfrom connection regions during anisotropic conductive connection andthis may cause connection failure. Therefore, the absolute thickness is6 μm or less.

The central region between adjacent conductive particles 4 is a regionwhich includes the midpoint of the distance between the adjacentconductive particles 4 and in which the thickness of thephotopolymerizable insulating resin layer 10 formed is small. The regionin proximity to a conductive particle 4 means a location near linesegments in contact with the conductive particle 4 and extending in thedirection of the thickness of the first connection layer 1.

The thickness t1 can be adjusted within above numerical range bycontrolling the diameter of the openings, the depth of the openings, thediameter of the conductive particles, the intervals between theopenings, a pressure value, the composition of the photopolymerizableinsulating resin, etc.

When the thickness of the resin layer containing the conductiveparticles varies largely in a plane direction and therefore the resinlayer is divided into sections as shown in FIG. 8, the thickness of theinsulating resin layer between conductive particles 4 can besubstantially zero (0). Substantially zero means that the dividedsections of the insulating resin layer that contain the conductiveparticles are present independently. In such a case, to achievefavorable connection reliability, favorable insulating properties, andfavorable particle capturing efficiency, it is preferable to control theminimum distances L¹, L², L³, L⁴ . . . between the perpendicularspassing through the centers of the conductive particles 4 and the pointsat which the thickness of the insulating resin layer is smallest.Specifically, when the minimum distances L¹, L², L³, L⁴ . . . are large,the relative amount of the resin in the first connection layer 1increases, and productivity is improved. In addition, the flow of theconductive particles 4 can be suppressed. When the minimum distances L¹,L², L³, L⁴ . . . are small, the relative amount of the resin in thefirst connection layer 1 decreases, and the distances between theparticles can be easily controlled. In other words, the accuracy of thepositional adjustment of the conductive particles can be improved.Preferred minimum distances L¹, L², L³, L⁴ . . . are within the range ofpreferably more than 0.5 times and less than 1.5 times the particlediameter of the conductive particles 4.

Various methods can be used as a method of reducing the thickness of theinsulating resin layer between conductive particles 4 to substantiallyzero, so long as the effects of the invention are not impaired. Forexample, one usable method includes scraping the surface of thephotopolymerizable insulating resin layer 10 formed in step (B) using,for example, a squeegee until the surface of the transfer die 20appears.

The conductive particles 4 may be embedded in the first connection layer1 as shown in FIG. 8. The degree of embedment, i.e., whether the depthof embedment is small or large, varies depending on the viscosity of thematerial of the first connection layer when it is formed, the shape andsize of the openings of the transfer die in which the conductiveparticles are arranged, etc. Particularly, the degree of embedment canbe controlled by changing the relation between the bottom diameter andopening diameter of the openings. Preferably, for example, the bottomdiameter is set to be 1.1 times or more and less than 2 times thediameter of the conductive particles, and the opening diameter is set tobe 1.3 times or more and less than 3 times the diameter of theconductive particles.

Conductive particles 4′ shown by dotted lines in FIG. 8 may be presentin a third connection layer 3, so long as the effects of the presentinvention are not impaired. Generally, the ratio of the number ofconductive particles present in the third connection layer 3 to thetotal number of conductive particles is preferably 1 to 50% and morepreferably 5 to 40%. Particularly, when the number of conductiveparticles 4 in the first connection layer 1 is substantially the same asthe number of conductive particles 4′ in the third connection layer 3,adjacent particles are present in different resin layers, and thereforeit is expected to have such an effect that a high conductive particledensity can be achieved locally while connection of a plurality ofconductive particles is suppressed. Therefore, as for the particlesarranged in a plane, the present invention also includes an embodimentin which conductive particles adjacent to given conductive particles arepresent and arranged in a layer different from the layer in which thegiven conductive particles are present.

The conductive particles 4′ present in the third connection layer 3 areobtained as follows. With conductive particles present on the surface ofthe transfer die in addition to the conductive particles accommodatedwithin the openings of the transfer die, the operation for forming thefirst connection layer is performed, and then the operation for formingthe third connection layer 3 is performed. It is practically difficultto avoid the presence of a certain amount or more of conductiveparticles on the surface etc. of the transfer die other than theopenings as described above. So long as these particles do not have suchan adverse effect that the performance of a product is impaired, theseparticles can reduce the occurrence of a defective product and thereforecontribute to an improvement in yield.

<Step (C)>

Next, as shown in FIG. 3, the first connection layer 1 is irradiatedwith ultraviolet rays through the light-transmitting transfer die 20.The photopolymerizable insulating resin 10 used for the first connectionlayer 1 is thereby polymerized and cured, so that the conductiveparticles 4 can be stably held in the first connection layer 1. Inaddition, the degree of cure of the photopolymerizable insulating resinin regions 1X that are shaded from the ultraviolet rays by theconductive particles 4 can be made lower than the degree of cure inregions 1Y around the regions 1X, and the ease of pushing the conductiveparticles 4 during anisotropic conductive connection can be improved. Inthis manner, while the positional displacement of the conductiveparticles during anisotropic conductive connection is prevented (i.e.,the particle capturing efficiency is improved), the ease of pushing theconductive particles can be improved, and the value of conductionresistance can be reduced, so that favorable conduction reliability canbe achieved.

The conditions of the ultraviolet irradiation can be appropriatelyselected from known conditions.

The degree of cure is a value defined as the rate of reduction in theamount of functional groups (for example, vinyl groups) that contributeto polymerization. Specifically, when the amount of vinyl groups presentafter curing is 20% of that before curing, the degree of cure is 80%.The amount of vinyl groups present can be measured by analyzing thecharacteristic absorption of vinyl groups in an infrared absorptionspectrum.

The above-defined degree of cure in the regions 1X is preferably 40 to80%, and the degree of cure in the regions 1Y is preferably 70 to 100%.

Preferably, the minimum melt viscosity of the first connection layer 1measured by a rheometer is higher than the minimum melt viscosity of asecond connection layer 2 and the minimum melt viscosity of the thirdconnection layer 3. Specifically, if the value of [the minimum meltviscosity (mPa·s) of the first connection layer 1]/[the minimum meltviscosity (mPa·s) of the second connection layer 2 or the thirdconnection layer 3] is too small, the particle capturing efficiencytends to deteriorate, and this causes an increase in the probability ofoccurrence of a short circuit. If the value is too large, the conductionreliability tends to deteriorate. Therefore, the above value ispreferably 1 to 1,000 and more preferably 4 to 400. A preferred minimummelt viscosity of each of the first connection layer 1, the secondconnection layer 2, and the third connection layer 3 will be described.If the minimum melt viscosity of the first connection layer 1 is toolow, the particle capturing efficiency tends to deteriorate. If theminimum melt viscosity thereof is too high, the value of the conductionresistance tends to become high. Therefore, the minimum melt viscosityof the first connection layer 1 is preferably 100 to 100,000 mPa·s andmore preferably 500 to 50,000 mPa·s. If the minimum melt viscosity ofthe second connection layer 2 and the third connection layer 3 is toolow, the resin tends to be squeezed out when the film is wound into areel. If the minimum melt viscosity is too high, the value of theconduction resistance tends to become high. Therefore, the minimum meltviscosity of the second connection layer 2 and the third connectionlayer 3 is preferably 0.1 to 10,000 mPa·s and more preferably 1 to 1,000mPa·s.

<Step (D)>

Next, as shown in FIG. 4, the release film 22 is removed from the firstconnection layer 1. No particular limitation is imposed on the removingmethod.

<Step (E)>

Then, as shown in FIG. 5, the second connection layer 2 formed mainly ofan insulating resin is formed on the surface of the first connectionlayer 1 that is opposite to the light-transmitting transfer die 20.

The second connection layer 2 is located on the surface of the firstconnection layer 1 from which no conductive particles 4 protrude and isgenerally a layer disposed on a terminal side for, for example, bumps ofan IC chip on which high positional alignment accuracy is required. Theregions 1X in the first connection layer 1 that are located between thesecond connection layer 2 and the conductive particles 4 have a lowdegree of cure, and this degree of cure is lower than the degree of cureof the other regions, i.e., the regions 1Y. Therefore, the regions 1Xare easily eliminated during anisotropic conductive connection. However,since the conductive particles are surrounded by the regions 1Y with ahigh degree of cure, unintended movement of the conductive particles isless likely to occur. Accordingly, while the positional displacement ofthe conductive particles is prevented (i.e., the particle capturingefficiency is improved), the ease of pushing the conductive particlescan be improved, and the value of the conduction resistance can bereduced. In addition, favorable conduction reliability can be achieved.

If the thickness of the second connection layer 2 is too small, it isfeared that conduction failure may occur due to lack of the amount ofresin for filling. If the thickness is too large, it is feared that theresin may be squeezed out during compression bonding, so that thecompression bonding machine may become dirty. Therefore, the thicknessof the second connection layer 2 is preferably 5 to 20 μm and morepreferably 8 to 15 μm.

<Step (F)>

Next, as shown in FIG. 6, the third connection layer 3 formed mainly ofan insulating resin is formed on the surface of the first connectionlayer 1 that is opposite to the second connection layer 2 (i.e., thesurface from which the conductive particles protrude) to thereby obtainan anisotropic conductive film 100. In this manner, the first connectionlayer and the third connection layer are formed with an undulatedboundary therebetween. In other words, the boundary has an undulatedshape or a bumpy shape. When such an undulated shape is applied tolayers present in the film as described above, the probability of anincrease in the area of contact with mainly a bump during bonding can beincreased, so that it is expected to improve the bonding strength. Whenthe undulation described above is present, it is more likely to obtainthe above-described state in which particles are present in the thirdconnection layer 3. This is because particles present in unridgedportions of the first connection layer 1 move to the third connectionlayer 3 during the process of forming the third connection layer 3.

The third connection layer 3 is generally disposed on a terminal sidefor, for example, solid electrodes of a circuit board on whichrelatively high alignment accuracy is not required. The third connectionlayer 3 is disposed on the side on which the conductive particles 4protrude from the first connection layer 1. Therefore, the conductiveparticles 4 in the first connection layer 1 immediately bump intoelectrodes of, for example, a circuit board and are deformed duringanisotropic conductive connection, so that the conductive particles 4are unlikely to move to unintended positions even when the insulatingresins flow during anisotropic conductive connection. Accordingly, whilethe positional displacement of the conductive particles is prevented(i.e., the particle capturing efficiency is improved), the ease ofpushing the conductive particles can be improved, and the value of theconduction resistance can be reduced. In addition, favorable conductionreliability can be achieved.

If the thickness of the third connection layer 3 is too small, it isfeared that application failure may occur when the film is temporarilyapplied to a second electronic component. If the thickness is too large,the value of the conduction resistance tends to become large. Therefore,the thickness of the third connection layer 3 is preferably 0.5 to 6 μmand more preferably 1 to 5 μm.

<<Materials Constituting First, Second and Third Connection Layers andConductive Particles>>

The anisotropic conductive film 100 shown in FIG. 6 and obtained by theproduction method of the present invention has a three-layer structurein which the first connection layer 1 is sandwiched between the secondconnection layer 2 and the third connection layer 3 which are eachformed mainly of an insulating resin, as described above. The firstconnection layer 1 has a structure in which the conductive particles 4are arranged in a single layer in a plane direction so as to protrudefrom the photopolymerizable insulating resin layer 10 toward the thirdconnection layer 3. The conductive particles 4 are disposed according tothe pattern of the openings of the transfer die used to produce theanisotropic conductive film 100. In this case, it is preferable that theconductive particles be arranged uniformly, i.e., arranged regularly inthe plane direction at regular intervals. In the structure of the firstconnection layer 1, the thickness t1 of the photopolymerizableinsulating resin layer in the central regions between adjacent ones ofthe conductive particles 4 is smaller than the thickness t2 of thephotopolymerizable insulating resin layer in the regions in proximity tothe conductive particles 4. Therefore, a conductive particle 4 notlocated between terminals to be connected and therefore not usedexhibits the behavior shown in FIG. 7. Specifically, portions of theinsulating resin layer that are disposed between conductive particles 4and have a relatively small thickness are melted and cut by heat andpressure applied during anisotropic conductive connection and cover theconductive particles 4 to thereby form a coating layer 1 d. Therefore,the occurrence of a short circuit is suppressed significantly.

<First Connection Layer>

Any known insulating resin layer can be appropriately used as thephotopolymerizable insulating resin layer 10 constituting theabove-described first connection layer 1. For example, the insulatingresin layer used can be a thermal- or photo-radical polymerizable resinlayer containing an acrylate compound and a thermal- or photo-radicalpolymerization initiator or a layer obtained by subjecting the thermal-or photo-radical polymerizable resin layer to thermal- or photo-radicalpolymerization; or a thermal- or photo-cationic or anionic polymerizableresin layer containing an epoxy compound and a thermal- orphoto-cationic or anionic polymerization initiator or a layer obtainedby subjecting the thermal- or photo-cationic or anionic polymerizableresin layer to thermal- or photo-cationic or anionic polymerization.

Of these, a thermal-radical polymerizable resin layer containing anacrylate compound and a thermal-radical radical polymerization initiatormay be used as the photopolymerizable insulating resin layer 10constituting the first connection layer 1. However, it is preferable touse a photo-radical polymerizable resin layer containing an acrylatecompound and a photo-radical polymerization initiator. In this case, thefirst connection layer 1 can be formed by irradiating the photo-radicalpolymerizable resin layer with ultraviolet rays to subject thephoto-radical polymerizable resin layer to photo-radical polymerization.

<Acrylate Compound>

The acrylate compound used for the photopolymerizable insulating resinlayer 10 constituting the first connection layer 1 may be any knownradical polymerizable acrylate. For example, a monofunctional(meth)acrylate (the term (meth)acrylate is meant to include acrylate andmethacrylate) or a bifunctional or higher functional (meth)acrylate maybe used. In the present invention, it is preferable to use apolyfunctional (meth)acrylate as at least part of an acrylic monomer, inorder to obtain a thermosetting adhesive.

Examples of the monofunctional (meth)acrylate may include methyl(meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl(meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl(meth) acrylate, 2-methylbutyl (meth) acrylate, n-pentyl (meth)acrylate,n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-methylhexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-butylhexyl(meth)acrylate, isooctyl (meth)acrylate, isopentyl (meth)acrylate,isononyl (meth)acrylate, isodecyl (meth)acrylate, isobornyl(meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate,phenoxy (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate,lauryl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate,and morpholine-4-yl (meth)acrylate. Examples of the bifunctional(meth)acrylate may include bisphenol F EO-modified di(meth)acrylate,bisphenol A EO-modified di(meth)acrylate, polypropylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, and dicyclopentadiene di(meth)acrylate.Examples of the trifunctional (meth)acrylate may includetrimethylolpropane tri(meth)acrylate, trimethylolpropane PO-modifiedtri(meth)acrylate, and isocyanuric acid ED-modified tri(meth)acrylate.Examples of the tetrafunctional or higher functional (meth)acrylate mayinclude dipentaerythritol penta(meth)acrylate, pentaerythritolhexa(meth)acrylate, pentaerythritol tetra(meth)acrylate, andditrimethylolpropane tetraacrylate. In addition, polyfunctional urethane(meth)acrylates can be used. Specific examples include: M1100, M1200,M1210, and M1600 (TOAGOSEI Co., Ltd.); and AH-600 and AT-600 (KYOEISHACHEMICAL Co., Ltd.).

If the content of the acrylate compound in the photopolymerizableinsulating resin layer 10 constituting the first connection layer 1 istoo small, the difference in minimum melt viscosity between the firstconnection layer 1 and the second connection layer 2 tends to becomesmall. If the content is too large, curing shrinkage tends to becomelarge, so that workability deteriorates. Therefore, the content of theacrylate compound is preferably 2 to 70% by mass and more preferably 10to 50% by mass.

<Photo-radical Polymerization Initiator>

The photo-radical polymerization initiator used may be appropriatelyselected from known photo-radical polymerization initiators. Examples ofsuch photo-radical polymerization initiators may includeacetophenone-based photopolymerization initiators, benzyl ketal-basedphotopolymerization initiators, and phosphorus-based photopolymerizationinitiators. Specific examples of the acetophenone-basedphotopolymerization initiators may include2-hydroxy-2-cyclohexylacetophenone (IRGACURE 184, manufactured by BASFJapan), α-hydroxy-α,α′-dimethylacetophenone (DAROCUR 1173, manufacturedby BASF Japan), 2,2-dimethoxy-2-phenylacetophenone (IRGACURE 651,manufactured by BASF Japan),4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone (DAROCUR 2959,manufactured by BASF Japan), and2-hydroxy-1-{4-[2-hydroxy-2-methyl-propionyl]-benzyl}phenyl)-2-methyl-propane-1-one(IRGACURE 127, manufactured by BASF Japan). Specific examples of thebenzyl ketal-based photopolymerization initiators may includebenzophenone, fluorenone, dibenzosuberone, 4-aminobenzophenone,4,4′-diaminobenzophenone, 4-hydroxybenzophenone, 4-chlorobenzophenone,and 4,4′-dichlorobenzophenone. In addition,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone-1 (IRGACURE369, manufactured by BASF Japan) can also be used. Specific examples ofthe phosphorus-based photopolymerization initiator may includebis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE 819,manufactured by BASF Japan) and(2,4,6-trimethylbenzoyl-diphenylphosphine oxide (DAROCUR TPO,manufactured by BASF Japan).

If the amount used of the photo-radical polymerization initiator basedon 100 parts by mass of the acrylate compound is too small,photo-radical polymerization tends not to proceed sufficiently. If theamount is too large, it is feared that the photo-radical polymerizationinitiator may cause a reduction in stiffness. Therefore the amount usedof the photo-radical polymerization initiator is preferably 0.1 to 25parts by mass and more preferably 0.5 to 15 parts by mass based on 100parts by mass of the acrylate compound.

<Thermal-radical Polymerization Initiator>

Examples of the thermal-radical polymerization initiator may includeorganic peroxides and azo-based compounds. Of these, organic peroxidesthat do not generate nitrogen causing air bubbles can be preferablyused.

Examples of the organic peroxides may include methyl ethyl ketoneperoxide, cyclohexanone peroxide, methylcyclohexanone peroxide,acetylacetone peroxide,1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane,1,1-bis(tert-butylperoxy)cyclohexane,1,1-bis(tert-hexylperoxy)3,3,5-trimethylcyclohexane,1,1-bis(tert-hexylperoxy) cyclohexane,1,1-bis(tert-butylperoxy)cyclododecane, isobutyl peroxide, lauroylperoxide, succinic acid peroxide, 3,5,5-trimethylhexanoyl peroxide,benzoyl peroxide, octanoyl peroxide, stearoyl peroxide, diisopropylperoxy dicarbonate, di-n-propyl peroxy dicarbonate, di-2-ethylhexylperoxy dicarbonate, di-2-ethoxyethyl peroxy dicarbonate,di-2-methoxybutyl peroxy dicarbonate, bis-(4-tert-butylcyclohexyl)peroxydicarbonate, (α,α-bis-neodecanoylperoxy)diisopropyl benzene,peroxyneodecanoic acid cumyl ester, peroxyneodecanoic acid octyl ester,peroxyneodecanoic acid hexyl ester, peroxyneodecanoic acid-tert-butylester, peroxypivalic acid-tert-hexyl ester, peroxypivalicacid-tert-butyl ester,2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane,1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, peroxy-2-ethylhexanoicacid-tert-hexyl ester, peroxy-2-ethylhexanoic acid-tert-butyl ester,peroxy-2-ethylhexanoic acid-cert-butyl ester, peroxy-3-methylpropionicacid-tert-butyl ester, peroxylauric acid-tert-butyl ester,tert-butylperoxy-3,5,5-trimethylhexanoate, tent-hexylperoxyisopropylmonocarbonate, tert-butylperoxyisopropyl carbonate,2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, peracetic acid-tert-butylester, perbenzoic acid-tert hexyl ester, and perbenzoic acid-tert-butylester. A reducing agent may be added to an organic peroxide, and themixture may be used as a redox-based polymerization initiator.

Examples of the azo-based compounds may include1,1-azobis(cyclohexane-1-carbonitrile),2,2′-azobis(2-methyl-butyronitrile), 2,2′-azobisbutyronitrile,2,2′-azobis(2,4-dimethyl-valeronitrile),2,2′-azobis(2,4-dimethyl-4-methoxyvaleronitrile),2,2′-azobis(2-amidino-propane)hydrochloride,2,2′-azobis[2-(5-methyl-2-imidazoline-2-yl)propane]hydrochloride,2,2′-azobis[2-(2-imidazoline-2-yl)propane]hydrochloride,2,2′-azobis[2-(5-methyl-2-imidazoline-2-yl)propane],2,2′-azobis[2-methyl-N-(1,1-bis(2-hydroxymethyl)-2-hydroxyethyl)propionamide],2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(2-methyl-propionamide)dihydrate, 4,4′-azobis(4-cyano-valericacid), 2,2′-azobis(2-hydroxymethylpropionitrile),2,2′-azobis(2-methylpropionic acid)dimethyl ester (dimethyl2,2′-azobis(2-methyl propionate)), and cyano-2-propylazoformamide.

If the amount used of the thermal-radical polymerization initiator istoo small, curing failure occurs. If the amount used is too large, thelife of a product decreases. Therefore, the amount used of thethermal-radical polymerization initiator is preferably 2 to 60 parts bymass and more preferably 5 to 40 parts by mass based on 100 parts bymass of the acrylate compound.

<Epoxy Compound>

The photopolymerizable insulating resin layer 10 constituting the firstconnection layer 1 may be formed from a thermal- or photo-cationic oranionic polymerizable resin layer containing an epoxy compound and athermal- or photo-cationic or anionic polymerization initiator or from alayer obtained by subjecting the thermal- or photo-cationic or anionicpolymerizable resin layer to thermal- or photo-radical polymerization.

When the photopolymerizable insulating resin layer 10 constituting thefirst connection layer 1 contains a thermal-cationic polymerizable resincontaining an epoxy compound and a thermal cationic polymerizationinitiator, the epoxy compound is preferably a compound or resin havingat least two epoxy groups in its molecule. These may be in liquid formor solid form. Specific examples thereof may include: glycidyl ethersobtained by reacting epichlorohydrin with polyphenols such as bisphenolA, bisphenol F, bisphenol S, hexahydrobisphenol A, tetramethylbisphenolA, diallylbisphenol A, hydroquinone, catechol, resorcin, cresol,tetrabromobisphenol A, trihydroxybiphenyl, benzophenone, bisresorcinol,bisphenol hexafluoroacetone, tetramethylbisphenol A,tetramethylbisphenol F, tris(hydroxyphenyl)methane, bixylenol, phenolnovolac, and cresol novolac; polyglycidyl ethers obtained by reactingepichlorohydrin with aliphatic polyols such as glycerin, neopentylglycol, ethylene glycol, propylene glycol, butylene glycol, hexyleneglycol, polyethylene glycol, and polypropylene glycol; glycidyl etheresters obtained by reacting epichlorohydrin with hydroxycarboxylic acidssuch as p-oxybenzoic acid and β-oxynaphthoic acid, and polyglycidylesters obtained from polycarboxylic acids such as phthalic acid,methylphthalic acid, isophthalic acid, terephthalic acid,tetrahydrophthalic acid, hexahydrophthalic acid,endomethylenetetrahydrophthalic acid, endomethylenehexahydrophthalicacid, trimellitic acid, and polymerized aliphatic acids; glycidyl aminoglycidyl ethers obtained from aminophenol and aminoalkyl phenols;glycidyl amino glycidyl esters obtained from aminobenzoic acid; glycidylamines obtained from aniline, toluidine, tribromoaniline,xylylenediamine, diaminocyclohexane, bisaminomethylcyclohexane,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, etc.; andknown epoxy resins such as epoxidized polyolefins. In addition,alicyclic epoxy compounds such as3,4-epoxycyclohexenylmethyl-3′,4′-epoxycyclohexenecarboxylate can alsobe used.

<Thermal Cationic Polymerization Initiator>

The thermal cationic polymerization initiator used may be any knownthermal cationic polymerization initiator for the epoxy compound. Forexample, a polymerization initiator that generates an acid capable ofcationically polymerizing a cationic polymerizable compound by heat canbe used, and known iodonium salts, sulfonium salts, phosphonium salts,ferrocenes, etc. can be used. Aromatic sulfonium salts exhibitingfavorable latency with respect to temperature can be preferably used.Preferred examples of the thermal cationic polymerization initiator mayinclude diphenyliodonium hexafluoroantimonate, diphenyliodoniumhexafluorophosphate, diphenyliodonium hexafluoroborate,triphenylsulfonium hexafluoroantimonate, triphenylsulfoniumhexafluorophosphate, and triphenylsulfonium hexafluoroborate. Specificexamples of the thermal cationic polymerization initiator may include:SP-150, SP-170, CP-66, and CP-77 manufactured by ADEKA Corporation;CI-2855 and CI-2639 manufactured by Nippon Soda Co., Ltd.; San-Aid SI-60and SI-80 manufactured by SANSHIN CHEMICAL INDUSTRY Co., Ltd.; andCYRACURE-UVI-6990 and UVI-6974 manufactured by Union CarbideCorporation.

If the amount added of the thermal cationic polymerization initiator istoo small, thermal cationic polymerization tends not to proceedsufficiently. If the amount added is too large, it is feared that thethermal cationic polymerization initiator may cause a reduction instiffness. Therefore, the amount of the thermal cationic polymerizationinitiator is preferably 0.1 to 25 parts by mass and more preferably 0.5to 15 parts by mass based on 100 parts by mass of the epoxy compound.

<Thermal Anionic Polymerization Initiator>

The thermal anionic polymerization initiator used may be any knownthermal anionic polymerization initiator for the epoxy compound. Forexample, a polymerization initiator that generates a base capable ofanionically polymerizing an anionic polymerizable compound by heat canbe used, and known aliphatic amine-based compounds, aromatic amine-basedcompounds, secondary amine-based compounds, tertiary amine-basedcompounds, imidazole-based compounds, polymercaptan-based compounds,boron trifluoride-amine complexes, dicyandiamide, organic acidhydrazides, etc. can be used. Encapsulated imidazole-based compoundsexhibiting favorable latency with respect to temperature can bepreferably used. Specific examples of the thermal anionic polymerizationinitiator include NOVACURE HX3941HP manufactured by Asahi KaseiE-materials Corporation.

If the amount added of the thermal anionic polymerization initiator istoo small, curing failure tends to occur. If the amount added is toolarge, the life of a product tends to decrease. Therefore, the amount ofthe thermal anionic polymerization initiator is preferably 2 to 60 partsby mass and more preferably 5 to 40 parts by mass based on 100 parts bymass of the epoxy compound.

<Photo-cationic Polymerization Initiator and Photo-anionicPolymerization Initiator>

The photo-cationic polymerization initiator or photo-anionicpolymerization initiator used for the epoxy compound may be any knownappropriate polymerization initiator.

<Conductive Particles>

Conductive particles appropriately selected from those used for knownanisotropic conductive films can be used as the conductive particles 4constituting the first connection layer 1. Examples of such conductiveparticles may include particles of metals such as nickel, cobalt,silver, copper, gold, and palladium and metal-coated resin particles.Two or more types of particles may be used in combination.

If the average particle diameter of the conductive particles 4 is toosmall, the conductive particles 4 cannot support variations in height oftraces, and conduction resistance tends to increase. If the averageparticle diameter is too large, the conductive particles 4 tend to causea short circuit. Therefore the average particle diameter of theconductive particles 4 is preferably 1 to 10 μm and more preferably 2 to6 μm. The average particle diameter can be measured using a generalparticle size distribution measuring device.

If the amount of the conductive particles 4 present in the firstconnection layer 1 is too small, the particle capturing efficiencydecreases, so that it is difficult to achieve anisotropic conductiveconnection. If the amount is too large, it is feared that a shortcircuit may occur. Therefore, the amount of the conductive particles 4is preferably 50 to 40,000 per square millimeter and more preferably 200to 20,000 per square millimeter.

<Additional Components in First Connection Layer>

If necessary, a film-forming resin such as a phenoxy resin, an epoxyresin, an unsaturated polyester resin, a saturated polyester resin, aurethane resin, a butadiene resin, a polyimide resin, a polyamide resin,or a polyolefin resin may also be used for the first connection layer 1.

When the photopolymerizable insulating resin layer 10 constituting thefirst connection layer 1 is a layer obtained by photo-radicalpolymerization of a photo-radical polymerizable resin layer composed ofan acrylate compound and a photo-radical polymerization initiator, it ispreferable that the photopolymerizable insulating resin layer 10 furthercontain an epoxy compound and a thermal cationic polymerizationinitiator. In this case, it is preferable that also the secondconnection layer 2 and the third connection layer 3 each be athermal-cationic polymerizable resin layer containing the epoxy compoundand the thermal cationic polymerization initiator, as described later.In this manner, interlayer peel strength can be improved.

In the first connection layer 1, it is preferable that the conductiveparticles 4 dig into the third connection layer 3 (i.e., the conductiveparticles 4 be exposed at the surface of the first connection layer 1)as shown in FIG. 6. This is because, if the conductive particles arefully embedded in the first connection layer 1, it is feared thatconduction reliability may deteriorate because of insufficientelimination of the insulating resin layer. If the degree of digging istoo small, the particle capturing efficiency tends to become small. Ifthe degree of digging is too large, the conduction resistance tends tobecome large. Therefore, the degree of digging is preferably 10 to 90%of the average particle diameter of the conductive particles and morepreferably 20 to 80%.

<Second Connection Layer and Third Connection Layer>

Each of the second connection layer 2 and the third connection layer 3is formed mainly of an insulating resin. The insulating resin used maybe appropriately selected from known insulating resins. The secondconnection layer 2 and the third connection layer 3 may be formed from amaterial similar to that for the photopolymerizable insulating resinlayer 10 in the first connection layer 1.

The second connection layer 2 is located on the first connection layer 1on the side on which the conductive particles 4 are disposed and isgenerally a layer disposed on a terminal side for, for example, bumps ofan IC chip on which high positional alignment accuracy is required. Thethird connection layer 3 is generally disposed on a terminal side for,for example, solid electrodes of a circuit board on which relativelyhigh alignment accuracy is not required.

If the thickness of the second connection layer 2 is too small, it isfeared that conduction failure may occur due to lack of the amount ofresin for filling. If the thickness is too large, it is feared that theresin may be squeezed out during compression bonding, so that thecompression bonding machine may become dirty. Therefore, the thicknessof the second connection layer 2 is preferably 5 to 20 μm and morepreferably 8 to 15 μm. If the thickness of the third connection layer 3is too small, it is feared that application failure may occur when thefilm is temporarily applied to a second electronic component. If thethickness is too large, the value of the conduction resistance tends tobecome large. Therefore, the thickness of the third connection layer 3is preferably 0.5 to 6 μm and more preferably 1 to 5 μm.

<<Applications of Anisotropic Conductive Film>>

The anisotropic conductive film obtained as described above can bepreferably used when a first electronic component such as an IC chip oran IC module and a second electronic component such as a flexiblesubstrate or a glass substrate are subjected to anisotropic conductiveconnection by heat or light. The connection structure obtained in themanner described above is also part of the present invention. In thiscase, it is preferable, in terms of improving connection reliability, totemporarily apply the anisotropic conductive film to the secondelectronic component such as a circuit board through the thirdconnection layer of the anisotropic conductive film, then mount thefirst electronic component such as an IC chip on the temporarily appliedanisotropic conductive film, and perform thermocompression bondingthrough the first electronic component. When light is used forconnection, thermocompression bonding may also be used in combination.

EXAMPLES

The present invention will next be described more specifically by way ofExamples.

Examples 1 to 6

A mixed solution containing, for example, an acrylate and aphoto-radical polymerization initiator at one of compositions shown inTABLE 1 was prepared using ethyl acetate or toluene so that the amountof solids was adjusted to 50% by mass. The prepared mixed solution wasapplied to a 50 μm-thick release-treated polyethylene terephthalate film(PET release film) to a dry thickness of 5 μm and dried in an oven at80° C. for 5 minutes to form a photo-radical polymerizable insulatingresin layer serving as a first connection layer.

Next, a glass-made ultraviolet ray-transmitting transfer die in whichcylindrical openings having a diameter of 5.5 μm and a depth of 4.5 μmwere provided at longitudinal and lateral intervals of 9 μm wasprepared. Then conductive particles with an average particle diameter of4 μm (Ni/Au-plated resin particles, AUL704, SEKISUI CHEMICAL Co., Ltd.)were accommodated in the openings such that one conductive particle wasplaced in each opening. The insulating resin layer for the firstconnection layer was placed on the transfer die so as to face itsopening-formed surface, and pressure was applied through the releasefilm under the conditions of 60° C. and 0.5 MPa to press the conductiveparticles into the insulating resin layer. An insulating resin layer wasthereby formed in which the thickness t1 of the photopolymerizableinsulating resin layer in central regions between adjacent ones of theconductive particles (see FIG. 2B) was smaller than the thickness t2 ofthe photopolymerizable insulating resin layer in regions in proximity tothe conductive particles (see FIG. 2B). TABLE 1 shows the results ofelectron microscope measurement of the thickness t1 of thephotopolymerizable insulating resin layer in the central regions betweenadjacent ones of the conductive particles and the thickness t2 of thephotopolymerizable insulating resin layer in the regions in proximity tothe conductive particles. The result of computation of the ratio of t1to t2 [t1/t2] is also shown.

Next, the photo-radical polymerizable insulating resin layer wasirradiated with ultraviolet rays having a wavelength of 365 nm at anintegrated light quantity of 4,000 mL/cm² through the ultravioletray-transmitting transfer die to thereby form a first connection layerwith the conductive particles secured on its surface.

Next, the PET release film adhering to the first connection layer waspeeled off to expose the first connection layer.

Next, a mixed solution containing, for example, a thermosetting resinand a latent curing agent was prepared using ethyl acetate or toluene sothat the amount of solids was adjusted to 50% by mass. The preparedmixed solution was applied to a 50 μm-thick PET release film to a drythickness of 12 μm and dried in an oven at 80° C. for 5 minutes to forma second connection layer. A third connection layer having a drythickness of 3 μm was formed using a similar procedure.

The second connection layer formed on the PET release film was laminatedonto the exposed surface of the above-obtained first connection layerunder the conditions of 60° C. and 0.5 MPa, and then the laminate wasremoved from the transfer die. Similarly, the third connection layer waslaminated onto the conductive particle-protruding surface of the firstconnection layer in the removed laminate to thereby obtain ananisotropic conductive film.

Comparative Example 1

A photo-radical polymerizable insulating resin layer used as a precursorlayer of the first connection layer was formed in the same manner as inExample 1.

Next, a glass-made ultraviolet ray-transmitting transfer die in whichcylindrical openings having a diameter of 5.5 μm and a depth of 4.5 μmwere provided at longitudinal and lateral intervals of 9 μm wasprepared.

Then conductive particles with an average particle diameter of 4 μm(Ni/Au-plated resin particles, AUL704, SEKISUI CHEMICAL Co., Ltd.) wereaccommodated in the openings such that one conductive particle wasplaced in each opening. The insulating resin layer for the firstconnection layer was placed on the transfer die so as to face itsopening-formed surface, and pressure was applied through the releasefilm under relatively weak conditions, i.e., 40° C. and 0.1 MPa, totransfer the conductive particles onto the insulating resin layer. Thefilm with the conductive particles transferred thereonto was removed,and then the conductive particles were fully pressed into the insulatingresin layer such that the surface of the resin layer became flat.

Next, the photo-radical polymerizable insulating resin layer with theconductive particles embedded therein was irradiated with ultravioletrays having a wavelength of 365 nm at an integrated light quantity of4,000 mL/cm² to thereby form a flat first connection layer.

Next, the PET release film adhering to the first connection layer waspeeled off to expose the first connection layer.

A 3 μm-thick third connection layer and a 12 μm-thick second connectionlayer produced in the same manner as in Example 1 were laminated ontothe first connection layer to obtain an anisotropic conductive film.

Comparative Example 2

A mixture prepared by dispersing the same conductive particles as thoseused in Example 1 in a resin composition for a first connection layershown in TABLE 1 was used to produce a 6 μm-thick resin film containingthe conductive particles. The amount of the conductive particles presentin the conductive particle-containing resin film was 20,000 per squaremillimeter. A 12 μm-thick second connection layer produced in the samemanner as in Example 1 was laminated on the above film under theconditions of 60° C. and 0.5 MPa to produce an anisotropic conductivefilm having a two-layer structure.

<Evaluation>

As for the uniform planar arrangement of the conductive particles ineach of the anisotropic conductive films obtained, when the uniformplanar arrangement was formed in the anisotropic conductive film, “YES”was assigned to “application of uniform planar arrangement of conductiveparticles” for the anisotropic conductive film. Otherwise, “NO” wasassigned. As for the thickness of the insulating resin layer in theregions in proximity to the conductive particles, when this thicknesswas larger than the thickness of the insulating resin layer in thecentral regions between the conductive particles (including a thicknessof 0), “YES” was assigned to “increase in thickness of insulating resinlayer in regions in proximity to conductive particles.” Otherwise, “NO”was assigned. The results are shown in TABLE 1. The number of layersforming each anisotropic conductive film is also shown.

Each of the obtained anisotropic conductive films was used to mount anIC chip with dimensions of 0.5×1.8×20.0 mm (bump size: 30×85 μm, bumpheight: 15 μm, bump pitch: 50 μm) on a glass circuit board (1737F) withdimensions of 0.5×50×30 mm manufactured by Corning Incorporated underthe conditions of 180° C., 80 MPa, and 5 seconds to thereby obtain asample connection structure. A cross section of the connection portionof the sample connection structure was observed under an electronmicroscope, and it was found that an insulating resin layer as shown inFIG. 7 was present around some of the conductive particles.

For each obtained sample connection structure, “minimum melt viscosity,”“particle capturing efficiency,” “conduction reliability,” and“insulating properties” were tested and evaluated in the mannersdescribed below. The results obtained are shown in TABLE 1.

“Minimum Melt Viscosity”

The minimum melt viscosity of each of the first connection layer andsecond connection layer constituting the sample connection structure wasmeasured using a rotary rheometer (TA Instruments) under the conditionsof a temperature rise rate of 10° C./min, a constant measurementpressure of 5 g, and a diameter of the measurement plate used of 8 mm.

“Particle Capturing Efficiency”

The ratio of “the amount of particles actually captured on the bumps inthe sample connection structure after heating and pressurization (actualmounting)” to “the theoretical amount of particles present on the bumpsin the sample connection structure before heating and pressurization”was determined using the following formula. Practically, the ratio ispreferably 40% or more.

Particle capturing efficiency (%)={[number of particles on bumps afterheating and pressurization]/[number of particles on bumps before heatingand pressurization]}×100

“Conduction Reliability”

The sample connection structure was left to stand in a high-temperaturehigh-humidity environment of 85° C. and 85% RH, and the initialconduction resistance value and the conduction resistance value after500 hours were measured. It is practically preferable that theresistance value be 10 Ω or less even after 500 hours.

“Insulating Properties”

The rate of occurrence of a short circuit in a comb-shaped TEG patternwith a spacing of 7.5 μm was determined. Practically, the rate ispreferably 100 ppm or less.

TABLE 1 Example 1 2 3 4 Application of Uniform Planar Arrangement ofConductive Particles Yes Yes Yes Yes Increase in Thickness of InsulatingResin Layer in Regions in proximity to Conductive Particles Yes Yes YesYes Thickness of Insulating Resin Layer in Central Regions betweenAdjacent Particles: t1 [μm] 3 3 3 3 Thickness of Insulating Resin Layerin Regions in proximity to Conductive Particles: t2 [μm] 6 6 6 6Thickness Ratio of insulating Resin Layer in First Connection Layer[t1/t2] 0.5 0.5 0.5 0.5 Number of Layers Consulting AnisotropicCondictive Film 3 3 3 3 First Phenoxy Resin (Parts By Mass) YP-50 NipponSteel Sumikin Chemical Co., Ltd. 60 60 60 60 Connection Acrylate (PartsBy Mass) EB600 Daicel-Alinex, Ltd. 40 40 Layer Photo-RadicalPolymerization IRGACURE 369 BASF Japan Ltd. 2 2 Initiator (Parts ByMass) Epoxy Resin (Parts By Mass) jER828 Mitsubishi Chemical Corporation40 40 Thermal Cationic Polymerization SI-60L Sanshin Chemical IndustryCo., Ltd. 2 2 Initiator (Parts By Mass) Minimum Melt Viscosity of First[mPa · s] After UV Irradiation for Examples 1 and 2 20000 20000 2000020000 Connection Layer Second Phenoxy Resin (Parts By Mass) YP-50 NipponSteel Sumikin Chemical Co., Ltd. 60 60 60 60 Connection Epoxy Resin(Parts By Mass) jER828 Mitsubishi Chemical Corporation 40 40 LayerThermal Cationic Polymerization SI-60L Sanshin Chemical Industry Co.,Ltd. 2 2 Initiator (Parts By Mass) Acrylate (Parts By Mass) EB600Daicel-Alinex, Ltd. 40 Organic Peroxide (Parts By Mass) PerhexylZ NCFCorporation 2 Minimum Melt Viscosity of Second [mPa · s] 500 500 500 500Connection Layer Third Phenoxy Resin (Parts By Mass) YP-50 Nippon SteelSumikin Chemical Co., Ltd. 60 60 60 60 Connection Epoxy Resin (Parts ByMass) jER828 Mitsubishi Chemical Corporation 40 40 Layer ThermalCationic Polymerization SI-60L Sanshin Chemical Industry Co., Ltd. 2 2Initiator (Parts By Mass) Acrylate (Parts By Mass) EB600 Daicel-Alinex,Ltd. 40 40 Organic Peroxide (Parts By Mass) PerhexylZ NCF Corporation 22 Minimum Melt Viscosity of Third [mPa · s] 500 500 500 500 ConnectionLayer [Minimum Melt Viscosity of First Connection Layer]/[Minimum 40 4040 40 Melt Viscosity of Second or Third Connection Layer] ConductionResistance Value (Ω) Initial 0.2 0.2 0.2 0.2 85° C., 85% RH, 500 hr 5.06.0 8.0 7.0 Insulating Properties(Rate of Occurrence [ppm] 30 30 30 30of Short Circuit) Particle Capturing Efficiency [%] 82.4 79.2 80.4 83.1Comparative Example Example 5 6 1 2 Application of Uniform PlanarArrangement of Conductive Particles Yes Yes Yes No Increase in Thicknessof Insulating Resin Layer in Regions in proximity to ConductiveParticles Yes Yes No No Thickness of Insulating Resin Layer in CentralRegions between Adjacent Particles: t1 [μm] 3 3 — — Thickness ofInsulating Resin Layer in Regions in proximity to Conductive Particles:t2 [μm] 6 6 — — Thickness Ratio of insulating Resin Layer in FirstConnection Layer [t1/t2] 0.5 0.5 — — Number of Layers ConsultingAnisotropic Condictive Film 3 3 3 3 First Phenoxy Resin (Parts By Mass)YP-50 Nippon Steel Sumikin Chemical Co., Ltd. 80 40 60 60 ConnectionAcrylate (Parts By Mass) EB600 Daicel-Alinex, Ltd. 20 60 40 40 LayerPhoto-Radical Polymerization IRGACURE BASF Japan Ltd. 2 2 2 2 Initiator(Parts By Mass) 369 Epoxy Resin (Parts By Mass) jER828 MitsubishiChemical Corporation Thermal Cationic Polymerization SI-60L SanshinChemical Industry Co., Ltd. Initiator (Parts By Mass) Minimum MeltViscosity of First [mPa · s] After UV Irradiation for Examples 1 and 22000 100000 20000 20000 Connection Layer Second Phenoxy Resin (Parts ByMass) YP-50 Nippon Steel Sumikin Chemical Co., Ltd. 60 80 60 60Connection Epoxy Resin (Parts By Mass) jER828 Mitsubishi ChemicalCorporation 40 20 40 40 Layer Thermal Cationic Polymerization SI-60LSanshin Chemical Industry Co., Ltd. 2 2 2 2 Initiator (Parts By Mass)Acrylate (Parts By Mass) EB600 Daicel-Alinex, Ltd. 40 Organic Peroxide(Parts By Mass) PerhexylZ NCF Corporation 2 Minimum Melt Viscosity ofSecond [mPa · s] 500 250 500 500 Connection Layer Third Phenoxy Resin(Parts By Mass) YP-50 Nippon Steel Sumikin Chemical Co., Ltd. 60 60 60Connection Epoxy Resin (Parts By Mass) jER828 Mitsubishi ChemicalCorporation 40 40 40 Layer Thermal Cationic Polymerization SI-60LSanshin Chemical Industry Co., Ltd. 2 2 2 Initiator (Parts By Mass)Acrylate (Parts By Mass) EB600 Daicel-Alinex, Ltd. Organic Peroxide(Parts By Mass) PerhexylZ NCF Corporation Minimum Melt Viscosity ofThird [mPa · s] 500 250 500 — Connection Layer [Minimum Melt Viscosityof First Connection Layer]/[Minimum 4 400 40 40 Melt Viscosity of Secondor Third Connection Layer] Conduction Resistance Value (Ω) Initial 0.20.2 2.0 0.2 85° C., 85% RH, 500 hr 5.0 8.0 50.0 5.0 InsulatingProperties(Rate of Occurrence [ppm] 100 10 30 3000 of Short Circuit)Particle Capturing Efficiency [%] 43.6 85.0 63.7 25.0

As can be seen from TABLE 1, for the anisotropic conductive films inExamples 1 to 6, the results for the evaluation of the particlecapturing efficiency, conduction reliability, and insulating propertieswere practically preferable. As can be seen from the results forExamples 1 to 4, when the curing systems of the first, second, and thirdconnection layers are the same, these layers are reacted with eachother. In this case, the ease of pushing the conductive particles isslightly reduced, and the conduction resistance value tends to increase.When the first connection layer is a cationic polymerization system,heat resistance is more improved than that in a radical polymerizationsystem. Also in this case, the ease of pushing the conductive particlesis slightly reduced, and the conduction resistance value tends toincrease.

However, in the anisotropic conductive film of Comparative Example 1,the thickness of the insulating resin layer in central regions betweenadjacent ones of the conductive particles in the first connection layerwas not smaller than the thickness of the insulating resin layer inregions in proximity to the conductive particles, so that the conductionresistance performance was reduced significantly. In the anisotropicconductive film in Comparative Example 2 having a conventional two-layerstructure, the particle capturing efficiency was reduced significantly,and the insulating properties were problematic.

Examples 7 to 8

Anisotropic conductive films were produced in the same manner as inExample 1 except that the conditions for pressurization through therelease film when the first connection layer was formed as shown inTABLE 2 were controlled so that the ratio of the thickness t1 of thephotopolymerizable insulating resin layer in the central regions betweenadjacent ones of the conductive particles (see FIG. 2B) to the thicknesst2 of the photopolymerizable insulating resin layer in the regions inproximity to the conductive particles (see FIG. 2B) [t1/t2] was one ofthe ratios in TABLE 2.

<Evaluation>

For each of the obtained anisotropic conductive films, the uniformplanar arrangement of the conductive particles was evaluated in the samemanner as in Example 1. The results obtained are shown in TABLE 2. Thenumber of layers constituting each anisotropic conductive film is alsoshown.

The obtained anisotropic conductive films were used to obtain sampleconnection structures in the same manner as in Example 1. A crosssection of the connection portion of each sample connection structurewas observed under an electron microscope, and it was found that aninsulating resin layer as shown in FIG. 7 was present around some of theconductive particles.

For each obtained sample connection structure, “minimum melt viscosity,”“particle capturing efficiency,” and “insulating properties” were testedand evaluated in the same manners as in Example 1, as described below.The “conduction reliability” was tested and evaluated in the followingmanner. The results obtained are shown in TABLE 2.

“Conduction Reliability”

The sample connection structure was left to stand in a high-temperaturehigh-humidity environment of 85° C. and 85% RH. The sample connectionstructure was removed at every 100 hour interval to check an increase inconduction resistance. The time at which the conduction resistanceexceeded 50 Ω was used as the time to failure. Practically, the time tofailure is preferably 1,000 hours or longer.

TABLE 2 Example 7 8 Application of Uniform Planar Arrangement ofConductive Particles Yes Yes Thickness of Insulating Resin Layer inCentral Regions between Adjacent Particles: t1 [μm] 1.5 4 Thickness ofInsulating Resin Layer in Regions in proximity to Conductive Particles:t2 [μm] 7.5 5 Thickness Ratio of Insulating Resin Layer in FirstConnection Layer [t1/t2] 0.2 0.8 Number of Layers ConstitutingAnisotropic Conductive Film 3 3 First Phenoxy Resin (Parts By Mass)YP-50 Nippon Steel Sumikin 60 60 Connection Chemical Co., Ltd, LayerAcrylate (Parts By Mass) EB600 Daicel-Allnex, Ltd. 40 40 Photo-RadicalPolymerization Initiator (Parts By Mass) IRGACURE 369 BASF Japan Ltd. 22 Minimum Melt Viscosity of First Connection Layer [mPa · s] 20000 20000Second Phenoxy Resin (Parts By Mass) YP-50 Nippon Steel Sumikin 60 60Connection Chemical Co., Ltd. Layer Epoxy Resin (Parts By Mass) jER.828Mitsubishi Chemical 40 40 Corporation Thermal Cationic PolymerizationInitiator (Parts By Mass) SI-60L Sanshin Chemical 2 2 Industry Co., Ltd.Minimum Melt Viscosity of Second Connection Layer [mPa · s] 500 500Third Phenoxy Resin (Parts By Mass) YP-50 Nippon Steel Sumikin 60 60Connection Chemical Co., Ltd. Layer Epoxy Resin (Parts By Mass) jER828Mitsubishi Chemical 40 40 Corporation Thermal Cationic PolymerizationInitiator (Parts By Mass) SI-60L Sanshin Chemical 2 2 Industry Co., Ltd.Minimum Melt Viscosity of Third Connection Layer [mPa · s] 500 500[Minimum Melt Viscosity of First Connection Layer]/[Minimum MeltViscosity of Second or Third Connection Layer] 40 40 ConductionReliability [hr] ≥1000 ≥1000 Insulating Properties (Rate of Occurrenceof Short Circuit) [ppm] 5 50 Particle Capturing Efficiency [%] 90 70

As can be seen from the results in TABLE 2, when the ratio of thethickness t1 of the photopolymerizable insulating resin layer in thecentral regions between adjacent ones of the conductive particles to thethickness t2 of the photopolymerizable insulating resin layer in theregions in proximity to the conductive particles (see FIG. 2B) [t1/t2]was 0.2 to 0.8, favorable results were obtained for each of theconduction reliability, the insulating properties, and the particlecapturing efficiency. It was found that as the value of [t1/t2]decreases, the insulating properties, in particular, tends to beimproved.

Examples 9 to 20

Anisotropic conductive films were produced in the same manner as inExample 1 except that the conditions for pressurization through therelease film when the first connection layer was formed as shown inTABLE 3 were controlled so that the ratio of the thickness t1 of thephotopolymerizable insulating resin layer in the central regions betweenadjacent ones of the conductive particles (see FIG. 2B) to the thicknesst2 of the photopolymerizable insulating resin layer in the regions inproximity to the conductive particles (see FIG. 2B) [t1/t2] was one ofthe ratios in TABLE 3. Specifically, the surface of the first connectionlayer was wiped as needed using known wiping means such as a squeegeeafter the formation of the first connection layer.

<Evaluation>

As for the uniform planar arrangement of the conductive particles ineach of the anisotropic conductive films obtained, when the uniformplanar arrangement was formed in the anisotropic conductive film, “YES”was assigned to “application of uniform planar arrangement of conductiveparticles” for the anisotropic conductive film. Otherwise, “NO” wasassigned. As for the thickness of the insulating resin layer in theregions in proximity to the conductive particles, when this thicknesswas larger than the thickness of the insulating resin layer in thecentral regions between the conductive particles (including a thicknessof 0), “YES” was assigned to “increase in thickness of insulating resinlayer in regions in proximity to conductive particles.” Otherwise, “NO”was assigned. The results are shown in TABLE 1 or 2. The number oflayers constituting each anisotropic conductive film is also shown.

For Examples 9 to 20, the ratio of the number of conductive particlespresent in the third connection layer to the total number of conductiveparticles in an area of 200 μm×200 μm was measured using an opticalmicroscope. The results obtained are shown in TABLE 3. The influence ofthe ratio of conductive particles present in the third connection layerwas examined. When the value of the ratio is 0, conductive particles arepresent only in the first connection layer. When the value of the ratiois 1, conductive particles are present only in the third connectionlayer 3.

The obtained anisotropic conductive films were used to obtain sampleconnection structures in the same manner as in Example 1. A crosssection of the connection portion of each sample connection structurewas observed under an electron microscope, and it was found that aninsulating resin layer as shown in FIG. 7 was present around some of theconductive particles.

For each obtained anisotropic conductive film, “minimum melt viscosity,”“particle capturing efficiency,” and “insulating properties” were testedand evaluated in the same manners as in Example 1, as described below.The “conduction reliability” was tested and evaluated in the followingmanner. The results obtained are shown in TABLE 3.

“Conduction Reliability”

The sample connection structure was left to stand in a high-temperaturehigh-humidity environment of 85° C. and 85% RH. The sample connectionstructure was removed at every 100 hour interval to check an increase inconduction resistance. The time at which the conduction resistanceexceeded 50 Ω was used as the time to failure. Practically, the time tofailure is preferably 1,000 hours or longer.

TABLE 3 Example 9 10 11 12 13 Application of Uniform Planar Arrangementof Conductive Particles Yes Yes Yes Yes Yes Thickness of InsulatingResin Layer in Central Regions between Adjacent Particles: t1 [μm] 0 1.53 4 0 Thickness of Insulating Resin Layer in Regions in proximity toConductive Particles: t2 [μm] 9 7.5 6 5 9 Thickness Ratio of InsulatingResin Layer in First Connection Layer [t1/t2] 0 0.2 0.5 0.8 0 NumberRatio of Particles Present in Third Connection Layer 0.5 0.1 0.2 0.30.55 Number of Layers Consulting Anisotropic Condictive Film 3 3 3 3 3First Phenoxy Resin (Parts By Mass) YP-50 Nippon Steel Sumikin 60 60 6060 60 Connection Chemical Co., Ltd. Layer Acrylate (Parts By Mass) EB600Daicel-Alinex, Ltd. 40 40 40 40 40 Photo-Radical Polymerization IRGACURE369 BASF Japan Ltd. 2 2 2 2 2 Initiator (Parts By Mass) Minimum MeltViscosity of First [mPa · s] 20000 20000 20000 20000 20000 ConnectionLayer Second Phenoxy Resin (Parts By Mass) YP-50 Nippon Steel Sumikin 6060 60 60 60 Connection Chemical Co., Ltd. Layer Epoxy Resin (Parts ByMass) jER828 Mitsubishi Chemical 40 40 40 40 40 Corporation ThermalCationic Polymerization SI-60L Sanshin Chemical 2 2 2 2 2 Initiator(Parts By Mass) Industry Co., Ltd. Minimum Melt Viscisity of Second [mPa· s] 500 500 500 500 500 Connection Layer Third Phenoxy Resin (Parts ByMass) YP-50 Nippon Steel Sumikin 60 60 60 60 60 Connection Chemical Co.,Ltd. Layer Epoxy Resin (Parts By Mass) jER828 Mitsubishi Chemical 40 4040 40 40 Corporation Thermal Cationic Polymerization SI-60L SanshinChemical 2 2 2 2 2 Initiator (Parts By Mass) Industry Co., Ltd. MinimumMelt Viscosity of Third [mPa · s] 500 500 500 500 500 Connection Layer[Minimum Melt Viscosity of First Connection Layer]/[Minimum 40 40 40 4040 Melt Viscosity of Second or Third Connection Layer] ConductionReliability [hr] ≥1000 ≥1000 ≥1000 ≥1000 ≥1000 Insulating Properties(Rate of Occurrence [ppm] 60 5 30 50 75 of Short Circuit) ParticleCapturing Efficiency [%] 70 90 82.4 70 70 Example 14 15 16 17Application of Uniform Planar Arrangement of Conductive Particles YesYes Yes Yes Thickness of Insulating Resin Layer in Central Regionsbetween Adjacent Particles: t1 [μm] 1.5 3 4 0 Thickness of InsulatingResin Layer in Regions in proximity to Conductive Particles: t2 [μm] 7.56 5 9 Thickness Ratio of Insulating Resin Layer in First ConnectionLayer [t1/t2] 0.2 0.5 0.8 0 Number Ratio of Particles Present in ThirdConnection Layer 0.5 0.45 0.4 0.05 Number of Layers ConsultingAnisotropic Condictive Film 3 3 3 3 First Phenoxy Resin (Parts By Mass)YP-50 Nippon Steel Sumikin 60 60 60 60 Connection Chemical Co., Ltd.Layer Acrylate (Parts By Mass) EB600 Daicel-Alinex, Ltd. 40 40 40 40Photo-Radical Polymerization IRGACURE 369 BASF Japan Ltd. 2 2 2 2Initiator (Parts By Mass) Minimum Melt Viscosity of First [mPa · s]20000 20000 20000 20000 Connection Layer Second Phenoxy Resin (Parts ByMass) YP-50 Nippon Steel Sumikin 60 60 60 60 Connection Chemical Co.,Ltd. Layer Epoxy Resin (Parts By Mass) jER828 Mitsubishi Chemical 40 4040 40 Corporation Thermal Cationic Polymerization SI-60L SanshinChemical 2 2 2 2 Initiator (Parts By Mass) Industry Co., Ltd. MinimumMelt Viscisity of Second [mPa · s] 500 500 500 500 Connection LayerThird Phenoxy Resin (Parts By Mass) YP-50 Nippon Steel Sumikin 60 60 6060 Connection Chemical Co., Ltd. Layer Epoxy Resin (Parts By Mass)jER828 Mitsubishi Chemical 40 40 40 40 Corporation Thermal CationicPolymerization SI-60L Sanshin Chemical 2 2 2 2 Initiator (Parts By Mass)Industry Co., Ltd. Minimum Melt Viscosity of Third [mPa · s] 500 500 500500 Connection Layer [Minimum Melt Viscosity of First ConnectionLayer]/[Minimum 40 40 40 40 Melt Viscosity of Second or Third ConnectionLayer] Conduction Reliability [hr] ≥1000 ≥1000 ≥1000 ≥1000 InsulatingProperties (Rate of Occurrence [ppm] 60 55 50 5 of Short Circuit)Particle Capturing Efficiency [%] 72 67 65 85 Example 18 19 20Application of Uniform Planar Arrangement of Conductive Particles YesYes Yes Thickness of Insulating Resin Layer in Central Regions betweenAdjacent Particles: t1 [μm] 1.5 3 4 Thickness of Insulating Resin Layerin Regions in proximity to Conductive Particles: t2 [μm] 7.5 6 5Thickness Ratio of Insulating Resin Layer in First Connection Layer[t1/t2] 0.2 0.5 0.8 Number Ratio of Particles Present in ThirdConnection Layer 0.03 0.01 ≥0.01 Number of Layers Consulting AnisotropicCondictive Film 3 3 3 First Phenoxy Resin (Parts By Mass) YP-50 NipponSteel Sumikin 60 60 60 Connection Chemical Co., Ltd. Layer Acrylate(Parts By Mass) EB600 Daicel-Alinex, Ltd. 40 40 40 Photo-RadicalPolymerization IRGACURE 369 BASF Japan Ltd. 2 2 2 Initiator (Parts ByMass) Minimum Melt Viscosity of First [mPa · s] 20000 20000 20000Connection Layer Second Phenoxy Resin (Parts By Mass) YP-50 Nippon SteelSumikin 60 60 60 Connection Chemical Co., Ltd. Layer Epoxy Resin (PartsBy Mass) jER828 Mitsubishi Chemical 40 40 40 Corporation ThermalCationic Polymerization SI-60L Sanshin Chemical 2 2 2 Initiator (PartsBy Mass) Industry Co., Ltd. Minimum Melt Viscisity of Second [mPa · s]500 500 500 Connection Layer Third Phenoxy Resin (Parts By Mass) YP-50Nippon Steel Sumikin 60 60 60 Connection Chemical Co., Ltd. Layer EpoxyResin (Parts By Mass) jER828 Mitsubishi Chemical 40 40 40 CorporationThermal Cationic Polymerization SI-60L Sanshin Chemical 2 2 2 Initiator(Parts By Mass) Industry Co., Ltd. Minimum Melt Viscosity of Third [mPa· s] 500 500 500 Connection Layer [Minimum Melt Viscosity of FirstConnection Layer]/[Minimum 40 40 40 Melt Viscosity of Second or ThirdConnection Layer] Conduction Reliability [hr] ≥1000 ≥1000 ≥1000Insulating Properties (Rate of Occurrence [ppm] 10 3 5 of Short Circuit)Particle Capturing Efficiency [%] 83 85 90

As can be seen from the results in TABLE 3, when the ratio of thethickness t1 of the photopolymerizable insulating resin layer in thecentral regions between adjacent ones of the conductive particles to thethickness t2 of the photopolymerizable insulating resin layer in theregions in proximity to the conductive particles (see FIG. 2B) [t1/t2]was 0.2 to 0.8, favorable results were obtained for each of theconduction reliability, the insulating properties, and the particlecapturing efficiency. It was found that as the value of [t1/t2]decreases, the insulating properties, in particular, tends to beimproved.

Even when the thickness t1 of the photopolymerizable insulating resinlayer was 0 (Examples 9, 13, and 17), favorable results were obtainedfor each of the conduction reliability, the insulating properties, andthe particle capturing efficiency when the thickness t2 of thephotopolymerizable insulating resin layer was set to be relativelylarge, i.e., preferably larger than the diameter of the conductiveparticles and less than three times the diameter of the conductiveparticles and more preferably 1.25 to 2.2 times. It was found that, whenthe thickness t2 of the photopolymerizable insulating resin layer isincreased, the ratio of the number of conductive particles present inthe third connection layer to the total number of conductive particlestends to increase. It was found that, even when more than half of theconductive particles are present in the third connection layer, noproblem occurs in the performance of the anisotropic conductive film.

INDUSTRIAL APPLICABILITY

In the anisotropic conductive film of the present invention having athree-layer structure in which the first connection layer is heldbetween the insulating second connection layer and the insulating thirdconnection layer, the first connection layer has a structure in whichthe conductive particles are arranged in a single layer in a planedirection of the insulating resin layer on its side facing the thirdconnection layer. In this structure, the thickness of the insulatingresin layer in the central regions between adjacent ones of theconductive particles is smaller than the thickness of the insulatingresin layer in the regions in proximity to the conductive particles.Therefore, with the anisotropic conductive film in which the conductiveparticles are arranged in a single layer, favorable connectionreliability, favorable insulating properties, and favorable particlecapturing efficiency can be achieved. The anisotropic conductive film isuseful for anisotropic conductive connection of an electronic componentsuch as an IC chip to a circuit board.

REFERENCE SIGNS LIST

-   1 first connection layer-   1X region having a low degree of cure in first connection layer-   1Y region having a high degree of cure in first connection layer-   2 second connection layer-   3 third connection layer-   4 conductive particle-   10 photopolymerizable insulating resin layer-   20 light-transmitting transfer die-   21 opening-   22 release film-   100 anisotropic conductive film

1-17. (canceled)
 18. An anisotropic conductive film comprising: a first connection layer formed mainly of insulating resin, the first connection layer having a structure in which conductive particles are present in a single layer without being in contact with each other, and insulating resin in vicinity of the conductive particles has undulation on a first side of the first connection layer; and a second connection layer formed mainly of insulating resin, the second connection layer being laminated on a second side of the first connection layer that is opposite the first side.
 19. The anisotropic conductive film according to claim 18, wherein the conductive particles are arranged.
 20. The anisotropic conductive film according to claim 18, wherein the conductive particles protrude from the first connection layer.
 21. The anisotropic conductive film according to claim 18, wherein the conductive particles are exposed on a surface of the first side of the first connection layer.
 22. The anisotropic conductive film according to claim 18, wherein insulating resin in vicinity of the conductive particles in the first connection layer is inclined with respect to a plane direction of the anisotropic conductive film.
 23. The anisotropic conductive film according to claim 18, wherein a third connection layer formed mainly of insulating resin is laminated on the first side of the first connection layer.
 24. The anisotropic conductive film according to claim 23, wherein the conductive particles dig into the third connection layer.
 25. A connection structure comprising a first electronic component and a second electronic component connected by anisotropic conductive connection using the anisotropic conductive film according to claim
 18. 26. A connection structure comprising a first electronic component and a second electronic component connected by anisotropic conductive connection using the anisotropic conductive film according to claim
 24. 27. A method of producing a connection structure, wherein a first electronic component and a second electronic component are connected by anisotropic conductive connection using the anisotropic conductive film according to claim 18, the method comprising: temporarily applying the anisotropic conductive film to the second electronic component through the first side of the first connection layer; mounting the first electronic component on the temporarily applied anisotropic conductive film; and performing thermocompression bonding through the first electronic component.
 28. A method of producing a connection structure, wherein a first electronic component and a second electronic component are connected by anisotropic conductive connection using the anisotropic conductive film according to claim 24, the method comprising: temporarily applying the anisotropic conductive film to the second electronic component through the third connection layer; mounting the first electronic component on the temporarily applied anisotropic conductive film; and performing thermocompression bonding through the first electronic component.
 29. An intermediate product film for producing an anisotropic conductive film having a first connection layer and a second connection layer laminated thereon, the first connection layer and the second connection layer being each formed mainly of insulating resin, comprising: the first connection layer having a structure in which conductive particles are present in a single layer without being in contact with each other, and insulating resin in vicinity of the conductive particles having undulation on a side of the first connection layer opposite the second connection layer.
 30. The intermediate product film according to claim 29, wherein the conductive particles are arranged. 